The Public Service Commission of the State of California requires timing and pulsing options in telephone branch exchanges of the type utilized in hotels or motels or central offices where controlled billing of local telephone calls is required. In addition to the more recent statutory requirements, it has been desirable to provide a means for automatic billing of local and toll telephone calls. Unfortunately, the prior art has been able to accomplish the required message unit billing by devices which are severley limited in versatility, complex and comprised of mechanical means prone to repetitive failures and in some instances prohibitively costly.
An example of an early timing arrangement for telephone calls is U.S. Pat. No. 2,488,797 on "Electrically Operated Timing Arrangement" issued to G. T. Baker on Nov. 22, 1949. This patent incorporates a timing arrangement comprised of rotary stepping switches and relays which are successively operated by the stepping switches to provide an elapsed time register. This type of timing output is not readily compatible with state of the art digital billing systems. An object of the present invention is to improve upon those types of systems by providing a message rate billing means which will produce pulses as a function of time that are readily processed by automated billing systems.
U.S. Pat. No. 2,596,308 on "Metering System For Telephonee" issued to Ernest Ungar on May 13, 1952 is a further example of prior means to achieve message rate billing via mechanical stepping switches. In this system the switches produce a plurality of pulses adapted to drive a metering circuit or a coin control circuit.
A more recent development in the art is U.S. Pat. No. 2,984,704 on "Automatic Determination Of Toll Call Charges" issued to N. S. Terry et al, on May 16, 1961. This system utilizes a plurality of relays and gas discharge lamps to monitor the time required for a toll call.
It is an object of the present invention to overcome the various hardware considerations present in systems of the above type by minimizing the number of mechanical switching components required.
The concept of using a pulse generator to create timed pulses for measuring the duration of a telephone call is presented in U.S. Pat. No. 3,573,378 on "Telephone Call Timing Circuit" issued to D. Leyburn on Apr. 6, 1971. This reference incorporates cascaded counting circuits adapted to count the pulses during a telephone call and increment a register when overtime charges are incurred. Systems such as this lack the ability to adapt to variations in billing rate charges.